I got this E2000 , I flashed it directly to tomato-E2000-NVRAM60K-1.28.905xRAF-ML-MIPSR2-075V-VPN.bin, no problem.
Then I downclocked cpu to 300 (telnet, nvram…), no problem, it changed to 300.
Then I flashed it to dualwan: tomato-K26USB-1.28.0542-MIPSR2-8M.trx, no problem.
Then I downclocked cpu to 300, this time something's wrong: if I login rooter with Iexplorer, CPU is always 354MB. But if I login with telnet, nvram get clkfreq, it shows "300,150,75".